If you bought Tilray (NASDAQ: TLRY) the day of its initial public offering (IPO) in July, you're now sitting on a whopping gain of 780%. If you bought the marijuana stock just a month ago, you're up more than 540%. Even if you're a late-comer to the Tilray train and scooped up some shares when the market opened on Monday of this week, you still have made a 65% return in only three days.Usually, I would say hold on to a stock for the long run.